[英]Combine to columns into one new column in mySQL
我在将2列合并到mySQL中的单列时遇到问题。
这是我想发生的事情:
由此
+----------------+----------------+----------+
| male | female | gender |
+----------------+----------------+----------+
| male | null | null |
+----------------+----------------+----------+
| male | null | null |
+----------------+----------------+----------+
| null | female | null |
+----------------+----------------+----------+
| male | null | null |
+----------------+----------------+----------+
对此
+----------+
| gender |
+----------+
| male |
+----------+
| male |
+----------+
| female |
+----------+
| male |
+----------+
我用过:
SELECT male,
female,
COALESCE(male, female) AS gender
FROM nrco_ldap
但“性别”列中没有任何反应。
您正在尝试更新现有的列,因此select
显然不是这样做的方法。 因此,您需要编写一个update
查询,如下所示:
update nrco_ldap
set gender = coalesce(male,female)
如果除了填充gender
列之外,您还想删除male
列和female
列,则还需要编写适当的drop语句,如下所示:
alter table nrco_ldap drop column male;
alter table nrco_ldap drop column female;
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